pre turbine pressure

[yoshimitsuspeed]

So on the MR2boards a discussion on the effects of altitude on boosted power led to a discussion on pre turbine pressure. Since I am running a DSM T25 I was wondering if people had measured their pre turbine pressure. I know it's not apples to apples since I'm only running 1.6 liters but it would give me an idea.
I will be upgrading to a rebuilt 14B soon so I would also be curios to see numbers for that, 16Gs and anything else for that matter.

 

[bastarddsm]

I doubt anyone has but ill bet you will see somewhere around what your running for boost as back pressure. It will start out lower than boost by a bit and then creep up to around a couple pounds above boost. This is coming from what I've seen on other engines.

 

[BoostedBeaver]

Exhaust back pressure will be different on every car. Anything that may restrict and or open up exhaust flow will have a influence. Turbine size exhaust diameter and converters/resonators are just a few examples. I have never measured the back pressure in my motor because my manifold is not taped. I have read that a 2:1 ratio makes for a good street turbo but once you break the 1:1 ratio is when big HP numbers come in. (Corky Bell)

 

[yoshimitsuspeed]

Wow I'm surprised there hasn't been more activity on this.

My pyrometer is tapped into the turbine inlet flange with 1/8 NPT so it would be pretty easy to find out what I get. It would be cool to compare the T25 to the 14B. I also wonder how hard it would be to find a cheap 7cm housing to compare. Don't think I would want one for DDing but it would be cool to see the effects it had. I'll try n remember to post up when I do. I'm sure some people here would be interested. I know the comparison wouldn't be that direct between my engine and the 4G63 but seeing the difference between the two turbos would still be cool.

 

[yoshimitsuspeed]

Just found this thread again.
In case anyone cares I thought I'd post what I found on my DSM T25.
This is on a 20 valve 1.6 liter 4AGE running 11:1 compression. I boost between 6 and 7 PSI. I also live around 6000 feet. Not sure if that would have much influence or not.
At highway speeds I got a couple PSI backpressure when not boosting. At 3500 RPM my boost to backpressure ratio was pretty close to 1:1. By redline I saw about 13 PSI PTBP at just 6ish PSI boost.
I suspect the turbine side is one of this turbos bigger bottlenecks.

If I ever get my 14B on I'll try to remember to post up results.

*edit*
Not sure if this had any effect but I did port the lip off the inlet side of the turbine and did a lot of blending into the housing as far as I could reach. I also tapered the outlet to match my 2.5" piping. That tapers out to a 3" turbo back exhaust system with a high flow cat and hooker aerochamber muffler.

 

[1qkfwd]

Ive read 2:1 and ive also read that 3:1 turbine pressure will make more than cranking up the boost. Me chasing the 14b record I do plan on logging that backpressure as soon as I get the manifold tapped.

 

[yoshimitsuspeed]

Ive read 2:1 and ive also read that 3:1 turbine pressure will make more than cranking up the boost.

I'm not really sure what you mean by this. Can you explain a little more?
Or maybe we are just looking at it backward from each other. Are you talking 2 or 3 times more pressure on the compressor side? That would be pretty impressive.
The less PTBP the better and the more power each PSI boost will gain you. On bigger turbos it's possible to get down to 1:1 or even better. I feel like I would gain a good bit of power if I could get that number down a bit. On the other hand I do love the T25 spool.
I might have to try a little more porting and see what it does.

 

[LandSpeed-DSM]

0.x:1 Drive/Boost Ratio lets you cam it more like an NA as well.

 

[Boostdriven]

If you're only going to run 6-7 psi of boost then 14b will be a better turbo for you. It has a larger exhaust wheel and if you port it like you did your t25 you should be able to get your exhaust pressure dropped to about 1.5:1 instead of 2:1 like you have right now and it will spool about the same as t25.

 

[yoshimitsuspeed]

0.x:1 Drive/Boost Ratio lets you cam it more like an NA as well.

This is somewhat true but you still have plenty of variation. For example, I see about 1:1 at 3500 RPM but over 2:1 at 7800 RPM. If I had a big turbo that maxed at 1:1 then it's quite likely in the lower RPM there would be more boost than PTBP. If you have too much overlap this could blow air and fuel through the open exhaust valve.

If you're only going to run 6-7 psi of boost then 14b will be a better turbo for you. It has a larger exhaust wheel and if you port it like you did your t25 you should be able to get your exhaust pressure dropped to about 1.5:1 instead of 2:1 like you have right now and it will spool about the same as t25.

Yeah, I have one waiting to go on. I have just been too lazy to finish welding up a couple cracks on the turbine housing, port it out and put it on.

 

[1qkfwd]

I'm not really sure what you mean by this. Can you explain a little more?
Or maybe we are just looking at it backward from each other. Are you talking 2 or 3 times more pressure on the compressor side? That would be pretty impressive.
The less PTBP the better and the more power each PSI boost will gain you. On bigger turbos it's possible to get down to 1:1 or even better. I feel like I would gain a good bit of power if I could get that number down a bit. On the other hand I do love the T25 spool.
I might have to try a little more porting and see what it does.

The turbine pressure ratio to boost. So for example a 2:1 ratio would be 20psi turbine backpressure to 10 psi of intake manifold boost. A 3:1 ratio would be 30psi to 10psi.

 

[LandSpeed-DSM]

This is somewhat true but you still have plenty of variation. For example, I see about 1:1 at 3500 RPM but over 2:1 at 7800 RPM. If I had a big turbo that maxed at 1:1 then it's quite likely in the lower RPM there would be more boost than PTBP. If you have too much overlap this could blow air and fuel through the open exhaust valve.

Conversely, you have exhaust reverting with higher Drive/Boost ratios.

>2:1 is not uncommon in OE applications. Your being down on displacement 20% vs. the original application of that turbo helps, but still has you at ~2.1:1 by redline even at very low bost.

PR and Massflow are also a big part of trying to determine if and where a given setup will cross the 1:1 Drive/Boost ratio.. I am running a ~95lb/min T4 footprint turbo with a head, intake and exhaust combo intended to make power from 5.5-10k+ rpm. Boost into the 30's should still have the ratio less than 1:1 with my particular configuration. If not, it's time for a 75-80mm compressor and a >85mm turbine.

Your T25 has a different purpose, so the higher ratio is not necessarily a bad thing if you want response over peak power.

 

[PieEyedPiper]

Ive read 2:1 and ive also read that 3:1 turbine pressure will make more than cranking up the boost. Me chasing the 14b record I do plan on logging that backpressure as soon as I get the manifold tapped.

The turbine pressure ratio to boost. So for example a 2:1 ratio would be 20psi turbine backpressure to 10 psi of intake manifold boost. A 3:1 ratio would be 30psi to 10psi.

Could you elaborate on these a little bit more?
It's sounding like you're saying a car will make more____ (power?) when the backpressure is increased compared to the increase in power that comes from more boost.
i.e. 31psi to 10psi will make more power than 30psi to 11psi. Maybe I'm just reading it wrong.

 

[1qkfwd]

Could you elaborate on these a little bit more?
It's sounding like you're saying a car will make more____ (power?) when the backpressure is increased compared to the increase in power that comes from more boost.
i.e. 31psi to 10psi will make more power than 30psi to 11psi. Maybe I'm just reading it wrong.

Sometimes on smaller turbo setups the drive ratio is a lot higher than what it should be. Im sure it goes way over a 3:1 ratio. Basically just saying that Ive heard its either 2:1 or 3:1 ratio will make more power than a higher ratio. Does that anwser that??

I have two cars im building and will be monitoring backpressures a lot with both. Should have more information of my own soon.

EDIT: I've been procrastinating long enough. Im pulling the manifold and tapping it before friday so I can get some Backpressure numbers on my 14B.

 

[BoostedBeaver]

I forgot that I even posted in this thread.

Anyway, I have actually tapped my FP Manifold and plan to wire the MAP in this afternoon if time permits. I already have the copper line so we will see where the HX35 in the BEP housing stands.

I learned a lot from a book called Maximum Boost by Corky Bell and it is a must read for enthusiast such as yourself. If you are taking the time to research it, this book has a lot of useful info that is backed up with test.

I should have some numbers soon and I will post the log.

Robert

 

[1qkfwd]

I forgot that I even posted in this thread.

Anyway, I have actually tapped my FP Manifold and plan to wire the MAP in this afternoon if time permits. I already have the copper line so we will see where the HX35 in the BEP housing stands.

I learned a lot from a book called Maximum Boost by Corky Bell and it is a must read for enthusiast such as yourself. If you are taking the time to research it, this book has a lot of useful info that is backed up with test.

I should have some numbers soon and I will post the log.

Robert

I've got that book to. Some stuff in there is out dated. Good for the beginner that doesnt know anything about turbos or how they are setup. I did see at summit the other day there is a newer turbo book thats more up to date. Not as much info though.

 

[yoshimitsuspeed]

Could you elaborate on these a little bit more?
It's sounding like you're saying a car will make more____ (power?) when the backpressure is increased

It's the other way around. You make more power when backpressure is decreased.
Backpressure makes the engine work harder to evacuate exhaust gasses. It also makes scavenging during valve overlap less efficient.
When the exhaust valve and intake valve are both open the low pressure wave from the exhaust leaving the cylinder actually sucks air and fuel into the cylinder for the next cycle. The higher the PTBP the less scavenging effect you get. If the exhaust side pressure is too much higher than the intake side it can actually push exhaust the other way into the intake. This is why turbo cars generally run shorter duration minimal overlap cams.
As said above if you have a properly designed and well balanced setup you could actually run pretty big higher overlap cams.
My motor was designed to be a high performance NA motor so it has pretty big cams for stock. It also has VVT which changes the intake timing and overlap. When I get it on the dyno I can actually set the VVt to come on and go off at the ideal times. If I change turbos it's very likely that point will change because of the intake to exhaust pressure ratio change.

I've got that book to. Some stuff in there is out dated. Good for the beginner that doesnt know anything about turbos or how they are setup. I did see at summit the other day there is a newer turbo book thats more up to date. Not as much info though.

Yeah, Maximum boost is a good primer for people getting started with turbo systems. I have learned far more from spending thousands of hours reading on the Internet. I still reccomend the book though. If nothing else it helps people learn to recognize the people who actually know what they are talking about and those who don't.

 

[PieEyedPiper]

It's the other way around. You make more power when backpressure is decreased.
Backpressure makes the engine work harder to evacuate exhaust gasses. It also makes scavenging during valve overlap less efficient.
When the exhaust valve and intake valve are both open the low pressure wave from the exhaust leaving the cylinder actually sucks air and fuel into the cylinder for the next cycle. The higher the PTBP the less scavenging effect you get. If the exhaust side pressure is too much higher than the intake side it can actually push exhaust the other way into the intake. This is why turbo cars generally run shorter duration minimal overlap cams.
As said above if you have a properly designed and well balanced setup you could actually run pretty big higher overlap cams.
My motor was designed to be a high performance NA motor so it has pretty big cams for stock. It also has VVT which changes the intake timing and overlap. When I get it on the dyno I can actually set the VVt to come on and go off at the ideal times. If I change turbos it's very likely that point will change because of the intake to exhaust pressure ratio change.



Yeah, Maximum boost is a good primer for people getting started with turbo systems. I have learned far more from spending thousands of hours reading on the Internet. I still reccomend the book though. If nothing else it helps people learn to recognize the people who actually know what they are talking about and those who don't.

Thanks. I know it's the other way around but when you hear the opposite with such certainty you have to stop and ask. In this case it was just difficulty in communication. Sometimes it's all straight in your head until the fingers hit the keyboard, .

I'd love to hear you talk to turboglenn about overlap. Keltalon, too. Those guys have some interesting ideas regarding overlap that you might find interesting at least. I think dsmonster might have made a few interesting points as well. But this was all some time ago.

 

[LandSpeed-DSM]

Thanks. I know it's the other way around but when you hear the opposite with such certainty you have to stop and ask. In this case it was just difficulty in communication. Sometimes it's all straight in your head until the fingers hit the keyboard, .

I'd love to hear you talk to turboglenn about overlap. Keltalon, too. Those guys have some interesting ideas regarding overlap that you might find interesting at least. I think dsmonster might have made a few interesting points as well. But this was all some time ago.

I've developed a bit of a pattern when I chime in on some of the "pick my turbo " threads that have popped up lately (constantly? ) and lean towards larger turbines and housings for a given setup than most, especially for pump gas applications. Then use adjustable gears to increase the I/E overlap window on a bigger than "conventional" turbo cam to breathe more like an efficient NA.

"Lag" is overblown. Especially if you know how to drive.. and a complimentary "larger" setup can and will have as much or more area under the curve in many cases at the same power as a smaller turbo thats being maxed out.


Experimenting with the different housings, cams, injectables, intercoolers and other VE mods while tracking Drive/Boost, EGT/IAT etc but keeping the Displacement and Turbo revealed a lot.

Using that to then play with multiple turbo and cam setups on the same displacement.

More power per PSI boost, you can run leaner and keep EGTs down with greater spark advance as a result of a more efficient setup.

 

[91stocker]

Kiggly's Mivec kit could come in handy with just such a thing.

 

[BoostedBeaver]

After configuring the LinBoost function in Link I got a 3 bar MAP configured to measure the back pressure for my bolt on HX35.

The sensor maxes out at 30.2 PSI which it hit at two points during this run. This means that I am running 1.62 PSI of back pressure for every pound of boost or a 1:1.62 ratio. Not the best but better than I expected. The screen shot below displays the results.

 

[1qkfwd]

After configuring the LinBoost function in Link I got a 3 bar MAP configured to measure the back pressure for my bolt on HX35.

The sensor maxes out at 30.2 PSI which it hit at two points during this run. This means that I am running 1.62 PSI of back pressure for every pound of boost or a 1:1.62 ratio. Not the best but better than I expected. The screen shot below displays the results.

Wow that's a smooth line. What input are you using? I just started logging backpressure right off the turbine housing for my 16g, it's pretty jagged.

 

[gofer]

From my understanding Rob's using the EGR input and his is tapped into the manifold itself, I wonder if your readings are more erratic since you're logging from the turbine housing?

 

[BoostedBeaver]

Gofer is correct, I am using the EGR input wired to a map that is tapped into the number one runner of the FP manifold with a few feet of copper hose and some fittings.

Robert

 

[tkelly27]

Here's a fun little toy for you all

*NEW* DTT DSM/EVO 8/9 EGR Turbo Back Pressure Plate - evolutionm.net

Too late for those who have already taken a drill and tap to their expensive manifolds : )